Films of ethyl cellulose



i atenied FILMS OF ETHYL. CELLULOSE Daniel D. Lanning, Williamsville, N. Y., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application March 2, 1940,

Serial No. 321,909

17 Claims. (Cl. 106-477) This invention relates to the stripping of dry cast cellulosic film's, especially continuous webs, from the casting surface.

as mono-lauryl-phthalate, for convenience called stripping agents, in organic solvent soluble organic cellulose substitution derivative dopes for facilitating separation of the cast film from the casting wheel.

Cellulosic materials which have been applied in organic liquid solution to the surface of such materials as wood, metals, ceramics, plastics and the like, and the solvent evaporated, possess considerable adhesion therefor. Such an inherent adhesion is very undesirable when the baseis employed only as a temporary support during the solvent removal, as in the casting or self-supporting film like sheet wrapping and similar material.

In general dry casting procedures involve the laying of a film of dope (solution of the cellulose substitution derivative) on to a casting wheel mounted for rotation and arranged for the removal of the solvent from the dope during its rotation. may include heating the surface of the wheel or surfaces adjacent thereto, together with devices such as fans for carrying the solvent or solventladen atmosphere away from the film. Ordinarily the speed of the wheel and the degree of heating are adjusted so that the desired amount More particularly it appertains to the incorporation of materials such The means for the solvent removal of solvent is removed in somewhat less than one revolution of the casting wheel. Nickel, chromium, stainless steel and other metals and alloys are generally used for surfaces of the casting wheels.

In attempting to carry out a continuous casting operation of this type with ethyl cellulose and similar cellulose ether dopes, it was found that the adhesion between the partially dried film and the casting surface was a frequent source of trouble. It caused the film to break or tear at the place where the film was being stripped from the wheel. This action was-especially troublesome at the edges of the film. Even when the film did not tear or break, distortion and deformation were quite common due to the high tension required for pulling the film away from the casting surface.

A type of material has now been discovered which greatly decreases the adhesion between such partially dried film and the metal casting surface. With the preferred members of the group the adhesion is reduced to such an extent that only a very slight tension is required to strip the film from the casting surface.

This invention had for an object the manufacture of transparent, strong and flexible organic solvent soluble cellulosic sheets or films which were undeformed and/or undistorted and/or unmarred, and the production of compositions of matter suitable for the casting thereof. A further object was to dry cast toluene-ethanol (:20) soluble ethyl cellulose into thin, strong, smooth, flexible sheets capable of being easily stripped from the casting wheel while retaining 5% to 15% of the solvent of the casting dope.

Further objects were to device a means of decreasing the adhesion between a dry cast, organic solvent soluble organic cellulose substitution derivative and the casting surface, to facilitate the removal of partially dried, dry cast, cellulose substitution derivatives from casting wheels and belts, and to find materials which could be added to cellulosic dry casting solutions to make removal of the film easy when only a small proportion of the solvent remains. A general advance in the art, and other objects which will appear hereinafter, are also contemplated.

It has now been discoveredthat mono-basic long chain alcohol esters may be incorporated in organic cellulose substitution derivative dry casting dopes with the result that the film formed therefrom can be easily and satisfactorily removed from the casting surface. The phthalate and phosphate esters from alcohols containing more than 6 carton atoms, are preferred.

From the following description and specific examples, in which are disclosed certain embodiments of the invention as well as details of what is believed to be the best mode for carrying out the invention, it will be apparent how the foregoing objects and related ends are accomplished. The parts are given by weight throughout the application, unless otherwise specified.

Example I To a solution containing 15% ethyl cellulose together with 15% (on the basis of the ethyl cellulose) tributyl phosphate (plasticizer) dissolved inan ethylene-dichloride methanol 80:20 solvent mixture, was added 3% (based on the ethyl cellulose present) mono-lauryl-phthalate. Film was cast from this solution onto a nickel surface and dried thereon. It possessed only a slight adhesion to the nickel surface, as compared to film cast from a similar solution to which no mono-lauryl-phthalate had been added. Equivalent results were obtained with other plasticizers, for example, triethylene glycol hexoate, di-

amyl-phthalate and butyl phthalyl butyl glycolate, andin the absence of plasticizer.

. Example II the casting wheel. It stripped very easily compared with a similar film containing no stripping agent. The film obtained was highly transparent and durable.

Example III A dope was prepared consisting of 15% ethyl cellu.lose together with 15% (on the basis of the ethyl cellulose present) butyl phthalyl butyl glycolate, and a solvent consisting of an ethylene dichloride-isopropyl alcohol 80:20 mixture. To this dope there was added 2% (based on the nonvolatile materials in the dope) of di-palmitylphosphate. A thin layer of this dope was cast on a nickel casting wheel and the volatile solvent evaporated. A glass-clear transparent film .001 inch thick resulted. It was easily stripped from the casting surface. Similar results were obtained with other mono-basic esters, particularly the phthalic and phosphoric acid esters of alcohols containing at least 7 carbon atoms.

Example IV A dope consisting of 17% of ethyl cellulose (48.0% ethoxyl content) together with 15% (on the basisof the ethyl cellulose) diethylene glycol dihexoate and a solvent consisting of an 80:20 mixture of toluene-ethanol, was cast in a continuous manner upon the polished surface of a large diameter chromium-surfaced drum. Be-. fore casting 3% (based on the film-formingmaterial and plasticizer content) of sodium amyl phthalate was incorporated in the dope. Upon evaporation of the solution a highly transparent and durable film was obtained, which was easily (compared with the same composition when no stripping agent was present) stripped from the casting drum. Ethyl benzyl cellulose operatedsimilarly to the ethyl cellulose.

Example V A film was prepared by evaporating the solvent from a composition consisting of 15% ethyl cellulose together with 15% (based on the ethyl cellulose) plasticizer and an 80:20 mixture of toluene-ethanol, in which had been incorporated 0.25% each of sodium mono-lauryl phthalate, P0- tassium mono-lauryl phthalate, calcium monolauryl phthalate, sodium mono-myristyl phthalate, potassium mono-myristyl phthalate, calcium mono-myristyl phthalate, sodium di-lauryl phosphate, potassium di-lauryl phosphate, calcium di-lauryl phosphate, sodium di-palmityl phosphate, potassium di-palmityl phosphate and calcium di-palmityl phosphate (on the basis of the ethyl cellulose plus the plasticizer) The resulting extremely durable film was stripped from, the metallic casting surface while it still contained 15% of the solvent. The stripping operation was easily carried out.

Example VI To.a solution containing 15% ethyl cellulose and 15% (based on the ethyl cellulose) di-amyl phthalate (plasticizer) dissolved in an 80:20 ethylene dichloride-methanol mixture, was added- 3% dilauryl phosphate (on the basis of the .ethyl cellulose). Film cast from this solution onto a nickel surface and dried possessed only a slight adhesion to the nickel surface when compared to film cast from a similar solution to which no dilauryl phosphate had been added.

Similar results were obtained when no plasticizer was present. A corresponding ease of stripping was obtained when the film was dried only to '8%-10%' solvent content and then removed from the casting surface.

' Example VII A dope consisting of:-

inwhich hadbeen incorporated 2% (based on the cellulosic components) mono-lauryl phthalate and 2% mono-myristyl phthalate, was cast continuously on the polished surface of a rotating nickel cylinder six feet in diameter. The volatile materlals were evaporated, and the resulting film stripped from the surface of the casting wheel.

The film, which had a thickness of .00088 inch, was very clear, and had excellent tear resistance.

' It was undeformed, unmarred, and undistorted.

It was stripped from the casting wheel very easily. Similar results were obtained with re-' lated mixtures.

Example VIII ethyl cellulose dissolved in a solvent mixture consisting of ethylene dischloride and 20% methanol, was added 3% (on the basis of the ethyl cellulose present) zinc lauryl phthalate. Film cast from this solution onto a nickel surface and dried possessed only a slight adhesion to the nickel surface when compared to film cast from a similar ethyl cellulose solution to which no zinc lauryl phthalate had been added.

The dope or cellulosic material solution containing the strip agents of the invention may be handled and cast in the same manner as the dry casting dopes previously known to the art.

The most marked decrease in adhesion be tween the film and the casting wheel surface has been noted when the casting surface was nickel.

In the preferred mode of operation the film is stripped from the casting wheel while it still contains 5% to 15% of the solvent. In all cases the major portion of the solvent should be removed before stripping the film.

This invention is not limited to the ethyl cellulose of the specific examples, although it peculiarly appertains thereto. In general it is, with considerable efficacy, applicable to all kinds of cellulosic compounds which are soluble in organic liquids (solvents), including cellulose esters, particularly the organic acid esters, such as cellulose acetate, cellulose propionate, cellulose butyrate and the like; mixed esters, such as cellulose aceto-propionate, cellulose aceto The advantageof incorporating in a casting butyrate and the like; cellulose ethers, such as methyl cellulose,-ethyl cellulose propyl cellulose. butyl cellulose, benzyl cellulose and the like; mixed ethers, such as ethyl benzyl cellulose and the like; and 'mixed cellulose ether esters such as ethyl cellulose acetate and the like.

Many plasticizers for dry cast cellulosic film have been suggested heretofore, and since the stripping agents of the invention are generally compatible therewith, it is only necessary to point out that the film may be plasticized in the conventional ways,-if desired. I

The mono-basic esters suitable for use in the operation of this invention, that is, for decreasing the adhesion between the dry cast ethyl cellulose film and the surface upon which the film is cast and dried (or partially dried), may be used in the form of their salts, that is to say, the esters function satisfactorily whether the cation of the carboxyl group is hydrogen or a metal. The preferred metals are from groups I and II of the periodic table of the elements, especially the alkali and alkaline earth metals such as sodium,

- potassium, calcium, zinc and the like. Sodium amyl phthalate, for example, is exceptionally good. v r The mono-basic esters comprehended by the present invention are those obtained from alcohols containing at least '7 carbon atoms. In some cases the five carbon atom alcohols have been found quite satisfactory, and this may .be regarded as a lower limit for the alcohol chain length. Preferably the alcohol contains 12 to 20 carbon atoms or more. Especially suitable for the purposes of the present invention are the mono-basic phthalic acid, adipic acid, and phosphoric acid esters. The results obtained with mono-lauryl phthalate, mono-myristyi phthalate, dilauryl phosphate, dimyristyl phosphate, diphenyl phosphate, diamyl phosphate, and dipalmityl phosphate are outstanding. Glycolate and hexoates may also be used.

.In the preferred embodiments of the invention the stripping agent is present in an amount within the range of 0.5% to by weight on the basis of the cellulosic material. Higher concentrations are not'excluded, and may be used in order to secure specific results.

The strip agents may be used singly or in any combination, and the invention is not limited to the specific materials listed above or in the specific examples.

The stripping agents of this invention may be incorporated in the casting dope in any desired manner. If preferred they may be predissolved and the solvent used for dissolving the cellulosic material. Ordinarily they are incorporated into the solvent simultaneously with the cellulosic substance. In some instances it has been found convenient to add the stripping agent to the solution of the cellulosic body.

Many of the advantages of the present invention will be apparent from the preceding portion of the specification; Specific mention may be made of the fact that by this invention it is possible to easily, speedily and satisfactorily remove the partially dried, dry cast organic solvent soluble-cellulose organic radical substitution derivative film from a metal or alloy casting wheel at elevated temperatures, and that all danger of tearing or deforming the dry cast film at the stripping point (or line) due to the pull required to separate the film from the casting surface has been removed.

solution a material which decreases the adhesion between the cellulosic film cast therefrom and the casting surface without undesirably au'ectmg I phosphate.

2. A dry cast film of material from the group consisting of cellulose ethers, cellulose esters and cellulose ether-esters containing 0.5% to 5% of a member of the group consisting of mono-basic phosphoric acid esters of monohydric alcohol containing at least 5 carbon atoms and their salts.

3. The product of claim 2 when the alcohol contains 12 to 20 carbon atoms.

4.- An organic solvent, dry casting solution of cellulose ether containing, as a strip agent, 0.5% to 5% (based on the cellulose substitution derivative) of dilauryl phosphate.

5. A plasticized, organic solvent soluble cellulosic ether sheet containing 5% to 15% of the casting solvent, and as a strip agent, 0.5% to 5% of dilauryl phosphate.

6. An organic solvent dry casting solution of 7. An organic solvent dry casting solution of.

ethyl cellulose containing, as a strip agent, 0.5%

to 5% (based on the ethyl cellulose) of dilauryl phosphate.

8. An organic solvent dry casting solution of cellulose ether containing, as a strip agent, 0.5% to 5% (based on the cellulose ether) of monobasic phosphoric acid ester of monohydric al-' cohol containing at least 5 carbon atoms.

9. An organic solvent dry casting solution of ethyl cellulose containing, as a strip agent, 0.5% to 5% (based on the ethyl cellulose) of monobasic phosphoric acid ester of monohydric alcohol containing 'at least 5 carbon atoms.

10. A dry casting solution of 80:20 ethylene dichloride-methanol mixture containing 15% ethyl cellulose and 15% (based on the ethyl cellulose) 'tributyl phosphate and 3% (based on the ethyl cellulose) of dilauryl phosphate.

11. Organic solvent soluble ethyl cellulose in the form of a dry cast self-supporting film to which has been added, prior to casting, 0.5% to 5% of mono-basic phosphoric acid ester of monohydric alcohol containing at least 5 carbon atoms.

12. Organic solvent soluble cellulose ether in the form of a dry cast self-supporting film to which has been added, prior to casting, 0.5% to 5% of mono-basic phosphoric acid ester of monohydric alcohol containing at least 5 carbon atoms.

comprises dissolving in an 80:20 ethylene dichloride-methanol mixture 15% ethyl cellulose and 3% (based on the ethyl cellulose) dilauryl phosphate.

17. The process of preparing a dry casting solution to be used in the preparation of thin, flexible, coherent, self-supporting cellulose ether film which comprises dissolving in an organic solvent 15% organic solvent soluble cellulose ether and 3% (based on the cellulose ether) mono-basic phosphoric acid ester of monohydrlc alcohol'contaming at least 5 carbon atoms.

DANIEL D. LANNING. 

